Hitherto, there has been used a camera wherein the exposure period is controlled by an electronic timing circuit comprising a photoelectric element which is so situated as to receive light reflected from the surface of photographic film in the camera. Such a camera has the advantage that the exposure is very exact, and that there is no need to compensate the .gamma.-character of the photoelectric element as described in our copending U.S. application Ser. No. 327,856 of Jan. 29, 1973, which is a continuation of U.S. application Ser. No. 54,130 of July 13, 1970, which is assigned to the assignee of the pending application. A further advantage resides in the fact that the information relating to the opening and closing of the shutter and aperture of the diaphragm is directly applied to the photoelectric element. However, such a camera has, on the other hand, shortcomings in that the exposure is liable to be excessive due to a time delay from a switching motion of the electronic circuit to an actual closing of the shutter, and that it is impossible to obtain an exposure period shorter than the above-mentioned delay period, and that it is impossible to give the camera user an indication of the exposure and an alarm against under-or over-exposures before the shutter is released, since the light measurement starts only after the opening of the shutter blades.
Moreover, as is well known, there are two kinds of shutters, namely lens shutters and focal-plane shutters. In the cameras with a focal plane shutter, a photosensitive element of the TTL system (through the lens system) is placed in front of a shutter screen, so that the photosensitive element can receive incident light before the shutter is opened. Accordingly, in such focal-plane shutter camera, the electronic exposure control system is responsive to an objective brightness detected prior to, simultaneously with, and subsequent to start of a shutter opening. Therefore, any delay in the photoelectric and electromechanic shutter control system does not adversely affect the exposure.
However, in the conventional lens shutter camera, the photosensitive element receives incident light only after the shutter opening. Therefore, in the lens-shutter cameras, any delay of the operation of the electromagnet causes adverse effect on the precision of the exposure obtained.